Conscious sleeping

There's an interesting way to demonstrate how the brain switches off unnecessary sensory inputs from registering in our consciousness.

Take, for instance, when we're reading a book in a quiet room where, say, a fridge is running. It's a fact that we soon stop hearing the sound of the compressor till someone brings it to our notice when we hear it for a short while again - till we start reading and it fades to silence once more.

There's an adaptive reason for this. If the brain were to be consciously registering every sensory input impinging on sense organs, our registry would soon overload with a lot of completely unwanted signals. Therefore, the brain registers for attention only those inputs that have immediate survival value while ignoring the rest.

Actually, there's an even more interesting twist to this. Sometimes, when the compressor just cycles off on its own and the fridge stops, we're suddenly jolted into attention by the lack of sound - which, of course, shouldn't happen if we weren't hearing it in the first place! It's as if the mind goes back briefly in time and yanks the last bit of sound from some limbo and forces it into memory so that we can contrast it with the subsequent silence.

Deep Zen meditators often ask themselves a similar question: am I conscious now? And, if I am because I've brought it to my awareness, was I conscious a moment ago when I hadn't? Just like the fridge stopping acts like a wake-up call, so do these questions. Because it isn't enough to be simply conscious; from time to time, one should be aware that one is conscious too.